Asish Basu | University of Texas at Arlington (original) (raw)

Papers by Asish Basu

We report on the first discovery of impact spherules in the PTB samples from Graphite Peak, Antar... more We report on the first discovery of impact spherules in the PTB samples from Graphite Peak, Antarctica.

Dynamic Failure of Materials, 1991

Gallstones most frequently are twinned, cracked, very large grained crystals of cholesterol that ... more Gallstones most frequently are twinned, cracked, very large grained crystals of cholesterol that have been grown in a saturated bile solution. In cross section, they are similar to spherulitic polymers although the composition of most gallstones is nearly pure cholesterol. The dynamic failure mechanism of “pulverization” during lithotripsy is at present only partially known. The literature suggest that cavitation next to the stone is the mechanism for stone destruction. Yet in vivo and in vitro observations show that many stones initially break approximately in half suggesting that internal flaws and dynamic loading, not cavitation with its surface removal processes, is the dominant mechanism. It is proposed that the stones break by crack propagation in a dominantly transient, reflected, stress field. Crack propagation and failure in gallstones is complicated by the large number of internal flaws, the low yield strength of the stones and the complex microstructure as it effects stress waves and dynamic fracture mechanisms. The physical properties of gallstones are presented from measurements of the elastic constants using literature wave speeds, hardness strengths and static fracture toughness. The static fracture properties have been measured on stones extracted from patients. These natural gallstones have very irregular shapes and a wide range of mechanical properties. While the surfaces of broken stones are very rough there is partial evidence of fatigue crack propagation. The cyclic crack propagation is probably due to stress intensity differences between compressive and tensile dynamic stresses on pre-existing cracks.

Geology, 2017

In recent years ophiolitic diamonds have been reported mostly from podiform chromitites. However,... more In recent years ophiolitic diamonds have been reported mostly from podiform chromitites. However, the mechanism of such diamond formation remains unknown. We report in situ diamond, graphite pseudomorphs after diamond crystals, and hydrocarbon (C-H) and hydrogen (H 2) fluid inclusions in ultrahigh-pressure (UHP) peridotitic minerals of the Nidar ophiolite, Indus suture zone. Diamond occurs as octahedral inclusion along with nitrogen (N 2) in orthoenstatite. Methane (CH 4) also occurs with UHP clinoenstatite (>8 GPa) in orthoenstatite. The graphite pseudomorphs after diamond crystals and primary hydrocarbon (C-H), and hydrogen (H 2) fluids are included in olivine. Oriented hematite (α-Fe 2 O 3) exsolutions are also present in the olivines, indicating a precursory β-Mg 2 SiO 4 phase of the host olivines. This assemblage of diamond, graphite, C-H and H 2 has not previously been reported from any ophiolitic peridotite. The hydrocarbon fluids in UHP clinoenstatites and retrogressed β-Mg 2 SiO 4 strongly suggest their source from the mantle transition zone or base of the upper mantle. We conclude that the peridotitic diamonds precipitated from C-H fluids during mantle upwelling beneath the Neo-Tethys Ocean spreading center.

International Geology Review, Dec 16, 2019

Ultra-high-pressure (UHP) peridotites found along collisional zones record rare information from ... more Ultra-high-pressure (UHP) peridotites found along collisional zones record rare information from deep within the Earth. However, the estimation of depth of origin for these UHP rocks has been controversial. A major controversy remains related to the conjectural proposition of mantle transition zone (410-660 km) origin of the Alpe Arami (AA) garnet peridotite massif in the Swiss Alps. In this contribution, we show micro-textural evidence of precursor majoritic garnet by documenting exsolved rutile, high-Al orthopyroxene, jadeite-rich clinopyroxene and olivine within the AA garnets in this peridotite. We also document an unforeseen texture of olivine with 'necklace' like enstatite corona in the kelyphite formed after decomposition of relict garnet. These olivines bear FeTiO 3 and Cr-spinel exsolution needles indicating retrogression from highpressure Mg 2 SiO 4. Thus, the occurrence of retrogressed high-pressure Mg 2 SiO 4 with enstatite corona in kelyphite suggests majorite breakdown to precipitate high-pressure Mg 2 SiO 4 near mantle transition zone (MTZ) depth. The SiO 2 released during decompression of majoritic garnets reacts with the high-pressure Mg 2 SiO 4 to produce the enstatite corona. Our documented microtextures show high-pressure Mg 2 SiO 4 are breakdown product of precursor majoritic garnet, indicating that these micro-textures of the AA peridotite massif are sourced from the mantle transition zone (MTZ).

Geology, Jun 9, 2017

Petroleum Science, 2020

Thermal maturity is commonly assessed by various geochemical screening methods (e.g., pyrolysis a... more Thermal maturity is commonly assessed by various geochemical screening methods (e.g., pyrolysis and organic petrology). In this contribution, we attempt to establish an alternative approach to estimating thermal maturity with Raman spectroscopy, using 24 North American oil shale samples with thermal maturity data generated by vitrinite reflectance (VRo%) and pyrolysis (Tmax)-based maturity calculation (VRe%). The representative shale samples are from the Haynesville (East Texas), Woodford (West Texas), Eagle Ford and Pearsall (South Texas) Formations, as well as Gothic, Mancos, and Niobrara Formation shales (all from Colorado). The Raman spectra of disordered carbonaceous matter (D1 and G bands separation) of these samples were directly obtained from the rock chips without prior sample preparation. Using the Gaussian and Lorentzian distribution approach, thermal maturities from VR were correlated with carbon G and D1. We found that the Raman band separation (RBS) displayed a better ...

Principles of Hydrogeology, Second Edition, 1999

Plate Tectonics, Ophiolites, and Societal Significance of Geology: A Celebration of the Career of Eldridge Moores, 2021

Ophiolite complexes represent fragments of ocean crust and mantle formed at spreading centers and... more Ophiolite complexes represent fragments of ocean crust and mantle formed at spreading centers and emplaced on land. The setting of their origin, whether at mid-ocean ridges, back-arc basins, or forearc basins has been debated. Geochemical classification of many ophiolite extrusive rocks reflect an approach interpreting their tectonic environment as the same as rocks with similar compositions formed in various modern oceanic settings. This approach has pointed to the formation of many ophiolitic extrusive rocks in a supra-subduction zone (SSZ) environment. Paradoxically, structural and stratigraphic evidence suggests that many apparent SSZ-produced ophiolite complexes are more consistent with mid-ocean ridge settings. Compositions of lavas in the southeastern Indian Ocean resemble those of modern SSZ environments and SSZ ophiolites, although Indian Ocean lavas clearly formed in a mid-ocean ridge setting. These facts suggest that an interpretation of the tectonic environment of ophiol...

Chemical Geology, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The Journal of Geology, Jul 1, 1982